The invention relates to automatic control systems for turbocharged Diesel engines in trucks. It relates, more particularly, to such control systems employed to provide for an automatic shutdown sequence in such engines.
In recent years the provision of Diesel engines for commercial trucks has increasingly been accompanied by the use of exhaust-driven turbosuperchargers for improvement of engine specific outputs and for a reduction of specific fuel consumption. The use of such accessory superchargers is relatively simple and, in comparison to the benefits obtained, relatively inexpensive.
One major dfference in the operation of Diesel truck engines has been due to the introduction of such superchargers, this is the requirement for specific shutdown sequences. The turbosupercharger is commonly a very sensitive device, operating at high temperatures yet possessing very little thermal mass of its own. Consequently, upon the cessation of engine operation very rapid cooling of the turbine disk is likely, and may result in damage to that component due to thermal stresses.
The several manufacturers of engines and turbosuperchargers indicate the need for engine operation at idle speed, or at some speed slightly above normal idle, for specified periods of time, to allow the turbine disk to attain a temperature level sufficiently low, so that shutdown thereafter will not induce damaging thermal stresses. In practice, however, the proper observance of such shutdown procedures is left to the skill and conscientiousness of the truckdriver, who may not be properly instructed in the appropriate procedures, or who may be unaware of the specific requirements of the rig he is entrusted with.
In practice, except for the relatively small number of drivers who conform to the required shutdown procedures, two alternatives emerge: either the engine is shut down immediately after the driver finishes his run, with the attendant danger of permanent damage to the supercharger, or, alternately, he remembers to leave the engine idling, but does so for an uncontrolled length of time. This latter alternative is also quite undesirable, since the lubricating system of the supercharger is generally not designed for extended periods of idle operation; in particular, the seals therein may become distorted and leak, thus resulting in eventual breakdown of the bearings.
It is, therefore, the primary object of the invention to provide the means, in the form of an automatic control system, whereby the proper operation of the engine during the shutdown procedure is removed from the control of the driver and the required periods of operation at the specified engine speeds is assured.
It is an additional object of the invention to provide such automatic control systems which are readily adapted to the several variations in engines and superchargers found in the industry, and which may be readily accomodated to the various control systems and electrical systems--12 and 24 volt operation, positive and negative grounds--met with.
It is a further object of the invention to provide such automatic control systems which are simple in construction, readily installed in commercial vehicles fitted with turbosupercharged Diesel engines, and trouble-free in operation.